Methods for improving uplink (UL) coverage, throughput and transmission latency are being investigated in Release 6 (R6) of the 3rd Generation Partnership Project (3GPP). In order to successfully implement these methods, scheduling and assigning of UL physical resources have been moved from a radio network controller (RNC) to a Node-B such that the Node-B can make decisions and manage UL radio resources on a short-term basis more efficiently than the RNC, even if the RNC retains overall control over the Node-B.
FIG. 1 is a block diagram of a conventional wireless communication system 100 configured in accordance with the present invention. The system 100 comprises a wireless transmit/receive unit (WTRU) 102, a Node-B 104 and an RNC 106. The RNC 106 controls overall enhanced uplink (EU) operation by configuring EU parameters for the Node-B 104 and the WTRU 102 such as initial transmit power level, maximum allowed EU transmit power or available channel resources per Node-B. Between the WTRU 102 and the Node-B 104, an E-DCH 108, a UL EU signaling channel 110 and a DL EU signaling channel 112 are established for supporting EU operations.
For E-DCH transmissions, the WTRU 102 sends a rate request to the Node-B 104 via the UL EU signaling channel 110. In response, the Node-B 104 sends a rate grant to the WTRU 102 via the DL EU signaling channel 112. After EU radio resources are allocated for the WTRU 102, the WTRU 102 transmits E-DCH data via the E-DCH 108. In response to the E-DCH transmissions, the Node-B 104 sends an acknowledgement (ACK) or non-acknowledgement (NACK) message for hybrid automatic repeat request (H-ARQ) operation via the DL EU signaling channel 112. The Node-B 104 may also respond with rate grants to the WTRU 102 in response to E-DCH data transmissions.
FIG. 2 is a block diagram of conventional protocol architecture of the WTRU 102. The protocol architecture of the WTRU 102 includes higher layers 202, a radio link control (RLC) layer 204, a medium access control (MAC) layer 206 and a physical layer (PHY) 208. The MAC layer 206 includes a dedicated channel MAC (MAC-d) 210 and an E-DCH MAC (MAC-e/es) 212. The MAC-e/es 212 handles all functions related to the transmission and reception of an E-DCH including, but not limited to, H-ARQ transmissions and retransmissions, priority of data, MAC-d/MAC-es multiplexing and transport format combination (TFC) selection.
One or more independent UL transmissions are processed on an E-DCH between a WTRU and a universal mobile telecommunication system (UMTS) terrestrial radio access network (UTRAN) within a common time interval. One example of this would be a MAC layer H-ARQ or a simple MAC layer automatic repeat request (ARQ) operation, where each individual transmission may require a different number of retransmissions to be successfully received by the UTRAN. This operation may result in a loss of transmission sequence at the MAC layer.
In accordance with the 3GPP standards, the transmission time interval (TTI) for the E-DCH is set to either 10 ms or 2 ms. In order to achieve a higher data rate and throughout, the operations of the E-DCH at the WTRU should be carefully designed to accommodate the required timing.